No, it's not a charter airline, it's a "semi-charter".
Corsair has two classes, and scheduled flights, but I think that you can order your tickets only via a travel agency...
But Corsair also operates many charter flights.

Corsair is a scheduled carrier since 2000 but does a lot harter flightson behalf of Nouvelles- Frontieres and other cies.
In the french west-indies and Reunion islands tickets can be purhased at Nouvelles- Frontieres or at any travel agencies.